Use of spike tires has been banned by law in Japan so as to prevent powder dust pollution resulting from the use of spike tires, and thus studless tires are now used instead of the spike tires in cold regions. Studless tires have been improved in their materials and designs for driving icy or snowy roads having a rougher surface than that of a usual road. For example, a rubber composition has been developed which contains diene rubber having excellent low-temperature properties and contains a softening agent in an increased amount so that a softening effect increases. Here, mineral oil is generally used as the softening agent in order to improve low-temperature properties.
If the amount of mineral oil is increased to improve low-temperature properties, abrasion resistance usually deteriorates. One way of solving such a problem is to change the mineral oil to aromatic oil; however, this way deteriorates low-temperature properties and thus makes it difficult to achieve sufficient performance on ice and snow. In contrast, combination use of aromatic oil and silica allows improvement of low-temperature properties without a decrease in abrasion resistance, but still cannot achieve sufficient levels of these performances. Further, improvement in wet grip performance, as well as performance on ice and snow and abrasion resistance, is also desired.
Patent Document 1, for example, discloses a rubber composition for a tread, which contains ingredients such as natural rubber, butadiene rubber, silica, and aromatic oil. This composition can still be improved in terms of achieving wet grip performance in addition to both abrasion resistance and the performance on ice and snow (low-temperature properties).    Patent Document 1: JP H06-240052 A